1. The Field of the Invention
This invention generally relates to systems and methods for broadcasting audio information from at least one transmission point to one or more reception points within a limited transmission space. More particularly, the present invention is directed to a system and method for simultaneously broadcasting a plurality of independent audio signals from at least one transmission point, through the transmission space, to a plurality of reception points and reproducing one of the audio signals selected by a user and providing the audio signal to the user.
2. The Background Art
In many types of both public and private gatherings there is a need to convey audio information from a first point to one or more remote reception points within the area of the gathering. For example, in educational, political, and religious gatherings it is often the case that the participants do not share a common language. Thus, it is often desirable to provide a simultaneous translation for each language spoken and understood by the participants. In such gatherings, for example, if the person addressing the group is speaking in English, it may be necessary to translate the speakers words into Spanish, German, and Russian for the various participants.
In order to ensure the least disruption and the best setting for proceedings where simultaneous translation into several languages must occur, it has been found to be most advantageous to locate the translators in a room which is acoustically isolated from the area where the proceedings are beind conducted and where the translators will be undistracted. In such an arrangement, the speaker's words are conveyed to the translator who can then simultaneously provide a verbal translation of what is being spoken.
Generally, each translator is provided with headphones which convey the words of the speaker who is addressing the proceedings. Each translator, located in her "own" booth or room, is also provided with a microphone into which she verbally provides the simultaneous translation. It will be appreciated that in many instances, several individual translators, for example, ten, twenty, or more, may be necessary.
It is a common practice to provide the translator's verbal translation to one or more headphones which can be worn by the participants. In this way, many different participants can hear the simultaneous translation of the speaker's words in a language which they can readily understand without distracting other participants.
Providing the proper translator's words to the participants in the past required running cables from a central switching area containing what is referred to in the art as a "patch bay." The central switching area has access to all of the translations and also to a headphone at each individual participant's listening station. Once it was known which listening station would require which translation, the patch bay was used to interconnect the translator's audio signal to the appropriate listening station.
When using such systems, users often complained of, or were hindered by, the cable connecting their headphones to the built-in cable system. Furthermore, installing a built-in cable system is an expensive procedure, particularly when retrofitting existing structures. Thus, as will be explained shortly, efforts in the past have been directed to eliminating the need for a cable connection between the participant's headphones and the translator.
Moreover, efforts have also been directed to allowing the user to roam anywhere within the room while still receiving the audio signal from the appropriate translator. Still further, many users often understand more than one language and would like the freedom to switch between several translators. Thus, it has been deemed desirable to allow any participant the option of listening to any one of a plurality of translators without requiring changing the interconnection at the central switching area.
In an effort to provide these advantages, various systems utilizing some type of electromagnetic communciation technique have been adopted. For example, one technique involves using large induction loops which are disposed in the proceedings room. Such induction loops may be implanted in the walls or floors supplying appropriately large amounts of modified current to the induction loops, which causes a modulated electromagnetic field to be radiated into the room. The radiated electromagnetic field (modulated by the translator's audio signal) is received by appropriately tuned coils located on the user's person. The received electromagnetic signals are demodulated and the audio information is passed onto headphones worn by the participant.
Unfortunately, induction loop communication systems have several disadvantages. Such disadvantages include extensive unacceptable cross-talk which occurs with any similar induction loop system in the vicinity, i.e., within the same building. Furthermore, unacceptable amounts of interference due to ambient electrical noise, and the cost of installing and maintaining the equipment, as well as its lack of an easily portable transmitter and difficult set up and take down procedure make such induction loop communications systems an undesirable choice in most situations.
In an effort to overcome some of the difficulties inherent in systems such as induction loop systems, cableless communication systems utilizing radio frequency (RF) techniques have been implemented. Most commonly, such RF-based systems utilize frequency modulation of a carrier in the very high frequency (VHF) band.
Significantly, the RF-based communication systems provided the important advantage of being able to simultaneously transmit more than one audio signal. Thus, in such a system each translator's audio signal might be transmitted on a different carrier frequency using well-known frequency multiplexing techniques and the user carries a battery-operated receiver. The user's receiver can then be turned just as he would a small transistor radio.
Use of RF-based communciation systems inherently have several drawbacks. First, the available space in the desirable portions (usually the VHF band) of the radio frequency spectrum is very limited. The crowding of the radio frequency spectrum is particularly severe in metropolitan areas where such systems are most often used. Communication equipment suitable for use in the present applications and using less crowded portions of the radio frequency spectrum is possible, but at a much greater cost and such equipment still encounters the other disadvantages mentioned below.
Second, as the number of audio channels to be simultaneously transmitted increases, the portion of the spectrum which must be allocated to operation of the communication system must also increase. Thus, the desirable attribute of including many channels in the system competes directly against the requirement of using as little radio spectrum space as possible.
Third, radio frequency signals are susceptible to interference from ambient electromagnetic noise sources such as motors and other electrical devices as well as from interference due to radio transmissions on adjacent frequencies.
Fourth, the use of a RF-based communication system in one room eliminates the possibility of using the same operating frequencies anywhere in the vicinity.
Fifth, a moving receiver located in a building will routinely experience multipath distortion resulting in unsatisfactory operation for the user.
The difficulties inherent in use of the previously available communication systems has prompted the development of systems utilizing optical signals to convey audio information. The availability of low cost and reliable optical devices, such as infrared emitting diodes (IREDs), solid state lasers, and semiconductor photodetectors, has allowed the optical portion of the electromagnetic spectrum to be utilized advantageously in communciation systems of the type described.
It should be understood that as used herein the term "optical signals" or "light" is intended to include any electromagnetic signal or emission above the radio frequency portion of the spectrum and below the X-ray portion of the electromagnetic spectrum. Significantly, the infrared portion of the spectrum is frequently used due to the availability of low cost, reliable electro-optical components.
In one previously available communication system which utilizes an infrared optical signal and has a capability of simultaneously transmitting a plurality of audio signals, the plurality of audio signals are frequency multiplexed to produce a modulating signal. The modulating signal is used to amplitude modulate one or more infrared emitting devices. The modulated infrared optical signal is broadcast into the proceedings room. A portable receiver carried by each user intercepts the optical signal, demodulates the signal, extracts the desired audio signal selected by the user, and conveys the selected audio signal to the user's headphones.
The use of optical signals (such as infrared signals) produces several important advantages over previous systems. One of the advantages which occurs through the use of optical signals is that the operation of identical systems in adjacent rooms is possible with no cross-talk between the systems since the optical signal cannot escape the proceeding room through its opaque walls. Also, due to the very small wavelength of optical signals, multipath distortion is virtually nonexistent. Moreover, the equipment necessary to transmit and receive infrared signals may be made extremely portable. Unfortunately, the use of frequency multiplexing techniques in order to impress a plurality of independent audio signals upon a single optical carrier requires tuned circuits which are complex, bulky, and require adjustment.
In view of the foregoing, it would be a significant advance in the art to provide a wireless communication system which could reliably provide cableless communication of a plurality of channels from a transmission point to a reception point. It would also be an advance in the art to provide a cableless communication system capable of conveying a plurality of channels with a minimum of crosstalk between each channel. It would be a further advance in the art to provide a multi-channel infrared cableless communication system which utilizes low cost components and may be easily transported, set up, and operated. Still another advance in the art would be to provide an infrared cableless communication system wherein much of the signal processing may be carried out by low cost, reliable digital circuitry.